The present invention relates an image forming apparatus that conducts image forming operations based on image data and is provided with a N-up printing mode in which a plurality of images represented by image data for a plurality of pages are printed by aligning them on a single paper sheet.
There has been well-known an image forming apparatus, such as a copier, a printer, a facsimile device, a Multifunctional Peripheral including abovementioned functions, etc., that conducts image-forming operations based on the image data, and is provided with the N-up printing mode which makes it possible not only to save a number of paper sheets to be consumed, but also to reduce the counting amount of printed paper sheets, by aligning a plurality of images represented by image data for a plurality of pages on a single paper sheet when conducting the image-forming operations. Although, sometimes, the N-up printing mode is called a N-in-1 mode, an Integration mode, etc., such the differently named modes have substantially the same function. It is applicable that the image data for a plurality of pages represent either a plurality of different images or a single image.
Tokkai 2003-101753 (Japanese Non-Examined Patent Publication) sets forth an image forming apparatus that is provided with an image integrating means to form an intensive image that includes a plurality of document images distributed on a single transfer material. According to the above image forming apparatus, the image integrating means reads a single document according to plural image processing methods established in advance, and makes it possible to put the image processing results together, so as to output the intensive image onto a single transfer material. The abovementioned feature makes it possible to eliminate cumbersome settings and operations to be conducted by the operator for repeating the copying operations by changing the image processing mode many times, etc., and to speedily confirm the contents of the image processing desired by the operator. Accordingly, it becomes possible not only to shorten the working hours and improve the maneuverability of the image forming apparatus, but also to reduce a number of unnecessary copies, resulting in an improvement of the economical aspects of the image forming apparatus.
In this connection, generally speaking in the N-up printing mode, it is possible to designate an arranging order of the images represented by the image data. For instance as shown in FIG. 10(a), FIG. 10(b), FIG. 10(c) and FIG. 10(d), various kinds of image arrangements, to be applied when four page images are arranged within a single paper sheet, will be detailed in the following. FIG. 10(a) shows a method for sequentially arranging the four page images in a vertical direction by setting the start position at the leading edge side relative to the conveying direction. FIG. 10(b) shows another method for sequentially arranging the four page images in a vertical direction by setting the start position at the trailing edge side relative to the conveying direction. FIG. 10(c) shows still another method for sequentially arranging the four page images in a horizontal direction by setting the start position at the leading edge side relative to the conveying direction. FIG. 10(d) shows yet another method for sequentially arranging the four page images in a horizontal direction by setting the start position at the trailing edge side relative to the conveying direction. It is possible for the user to designate any one of the abovementioned four kinds of image arrangements.
In the light-material printing market, sometimes, the abovementioned N-up printing mode is employed for reducing the printing cost, in such a manner that the same images for plural pages are printed on a single transfer paper, and then, the printed images are cut into the plural pages by employing an offline post processing apparatus. However, if there exists in the image forming section a density inclination along the main-scanning direction from the leading edge to the trailing edge of the single transfer paper concerned, the density of the images disposed at the leading edge side is different from that disposed at the trailing edge side. Since the same images are printed on the single transfer paper, the color and quality differences between the images can be considerably recognized and cause the deterioration of the printing quality. Further, even when the different images are printed, the color and quality differences between them, caused by the density inclination, are sensible for the user, resulting in the deterioration of the printing quality.
Generally speaking, in the image forming section, a toner image is formed on the photoreceptor drum according to the steps of: uniformly charging a circumferential surface of the photoreceptor drum by activating the charging section; conducting the exposure scanning operation to form a latent image by activating the image writing section; and applying the reversible developing operation to the latent image with toner, so as to form the toner image on the circumferential surface of the photoreceptor drum. Then, the image-forming operation is achieved by transferring the toner image onto the paper sheet. Accordingly, the cause of the density inclination mentioned in the above varies in a wide range of factors in the main-scanning direction, such as mechanical variations in the image writing section, a longitudinal inclination of the charging electrode relative to the circumferential surface of the photoreceptor drum, etc. Therefore, it has been a difficult problem how to cope with the density inclination when it happens.